1. Field of the Invention
The present invention relates to a field of chemical analysis, and more specifically to a mass spectrometer that uses atmospheric pressure chemical ionization.
2. Description of the Prior Art
Pollution by dioxins has become a serious social issue, and various measures have been taken. In particular, since the major source of dioxins newly released in environment is waste incinerators, monitoring of exhaust gas from incinerators has been intensified.
In a conventional method of measuring dioxin contained in the exhaust gas from incinerators, quantitative analyses are performed for each isomer using high-resolution gas chromatograph/mass spectrometer (hereafter abbreviated as GC/MS) after complicated pre-treatments. This is because the toxicity of dioxins differs depending on isomers. The resulting measurements are converted to the weight of 2,3,7,8-tetrachlorodibenzo-p-dioxin, and recorded as a toxicity equivalent quantity (hereafter abbreviated as TEQ). Although this method enables accurate measurement, it is the present situation that the analysis requires much labor, and that it takes nearly one month before the result is obtained. The cost for the analysis of one sample is as high as about ¥300,000.
The reason why the complicated pre-treatment is required in the conventional technique is the use of electron impact (hereafter abbreviated as EI) as the ion source of the mass spectrometer. EI is a method of forming ions by the impact of electrons by radiating electron beams on a sample substance, and is a general-purpose ionizing method. On the other hand EI causes the decomposition of molecules easily, and if a plurality of substances reach the ion source at the same time, the mass spectra become complicated, and may cause erroneous measurements. Therefore, complicated operations are required to remove impurities and separate every each component.
As described above, since the precision analysis of dioxins requires much labor and cost, frequent analyses are difficult. Therefore, the exhaust gas from a waste incinerator is analyzed twice a year. In each analysis, sampling is performed for 4 hours. However, the quantity of dioxins in exhaust gas is significantly depends on combustion conditions, analyses performed twice a year do not always determine the quantity of dioxins released from the incinerator for a long period of time.
In order to estimate the quantity of dioxins more easily, other indices that correlates the quantity of dioxins, for example a quick measurement of the concentration of chlorophenols or chlorobenzenes considered to be dioxin precursors, have been studied. This is the effort to decrease the quantity of produced dioxins by estimating the quantity of dioxins contained in exhaust gas from the measurement of dioxin precursors, and feeding back the estimated value to the combustion controller. However, since the quantity of dioxin precursors in exhaust gas is 103 to 104 times the quantity of dioxins, the correlation between the concentration of precursors and the concentration of dioxin is not sufficiently high.
Therefore, the present inventors noticed the total quantity of dioxins, which has a high correlation to TQC, and started the development of a system for monitoring the quantity of dioxins released from incinerators in environment for a long period of time by easily measuring the total quantity of dioxins. The object of the present invention is to provide a mass spectrometer favorably used for measuring the total quantity of dioxins.
The present invention provides a mass spectrometer having a high sensitivity, including a sample supply tube for supplying a sample solution containing a sample to be measured, a nebulizer for nebulizing the sample solution supplied from the sample supply tube, an ion source including a needle electrode for ionizing the sample nebulized and vaporized in the nebulizer, and a mass analyzer for analyzing ions formed in the ion source by mixing a carrier gas with the nebulized sample or the sample vaporized by the vaporizer to supply the mixed sample to the ion source. The present invention also provides a mass spectrometer suitable for measuring the total quantity of dioxins, wherein the moving direction of the sample is made opposite to the moving direction of ions at the tip of the needle electrode.
An ion source and a mass spectrometer of the present invention have the following features:
(1) An ion source including: a nebulizer for nebulizing a sample solution; a vaporizer for vaporizing the sample nebulized by the nebulizer; a gas mixer for mixing a carrier gas with the sample nebulized by the nebulizer or vaporized by the vaporizer; and a discharge chamber having a gas entrance and a gas exit through which the carrier-gas mixed sample flows in and flows out, a needle electrode that generates corona discharge, and an aperture for taking out the ionized sample.
(2) The ion source according to the above-described (1), further including a mixing rate controller for controlling the flow rate of the sample solution supplied to the nebulizer, and the mixing rate of the carrier gas supplied to the gas mixer.
(3) The ion source according to the above-described (2), wherein the mixing rate controller controls (the flow rate of the carrier gas)/(the flow rate of the sample solution) to a predetermined value between 2,500 and 15,000.
(4) The ion source according to the above-described (2), wherein the mixing rate controller controls (the flow rate of the carrier gas)/(the flow rate of the sample solution) to a predetermined value between 5,000 and 8,000.
(5) The ion source according to the above-described (1), wherein the gas entrance of the discharge chamber is also used as an aperture for taking out the ionized sample.
(6) The ion source according to the above-described (1), further including a flow path for bypassing through the discharge chamber a part of the carrier-gas mixed sample supplied from the gas mixer.
(7) A mass spectrometer including: a nebulizer for nebulizing a sample solution; a vaporizer for vaporizing the sample nebulized by the nebulizer; a mixer for mixing a carrier gas with the sample nebulized by the nebulizer or vaporized by the vaporizer; a discharge chamber having a gas entrance and a gas exit through which the carrier-gas mixed sample flows in and flows out, a needle electrode that generates corona discharge therein, and an aperture for taking out the ionized sample; and a mass analyzer wherein ions taken out of the aperture in the discharge chamber are introduced.
(8) The mass spectrometer according to the above-described (7), further including a mixing rate controller for controlling the flow rate of the sample solution supplied to the nebulizer, and the mixing rate of the carrier gas supplied to the gas mixer.
(9) The mass spectrometer according to the above-described (8), wherein the mixing rate controller controls (the flow rate of the carrier gas)/(the flow rate of the sample solution) to a predetermined value between 2,500 and 25,000.
(10) The mass spectrometer according to the above-described (8), wherein the mixing rate controller controls (the flow rate of the carrier gas)/(the flow rate of the sample solution) to a predetermined value between 5,000 and 8,000.
(11) The mass spectrometer according to the above-described (7), wherein the gas entrance of the discharge chamber is also used as an aperture for taking out the ionized sample.
(12) The mass spectrometer according to the above-described (7), further comprising a flow path for bypassing through the discharge chamber a part of the carrier-gas mixed sample supplied from the gas mixer.